At Thu, 1 Apr 2021 21:03:37 +0200, Manuel Bouyer <bouyer%antioche.eu.org@localhost> wrote: Subject: UVM behavior under memory pressure > > Of course the system is very slow > Shouldn't UVM choose, in this case, to reclaim pages from the file cache > for the process data ? > I'm using the default vm.* sysctl values. I almost never use the default vm.* values. I would guess the main problem for your system's memory requirements, at the time you showed it, is that the default for vm.anonmin is way too low and so raising vm.anonmin might help. If vm.anonmin isn't high enough then the pager won't sacrifice other requirements already in play for anon pages. Lowering vm.filemax (and maybe also vm.filemin) might also help since your system, at that time, appeared to be doing far less I/O on large numbers of files than, say, a web server or a compile server might be doing. However with almost 3G dedicated to the file cache it would seem your system did recently trawl through a lot of file data, and so with a lower vm.filemax less of it would have been kept as pressure for other types of memory increased. Here are the values I use, with comments about why, from my default /etc/sysctl.conf. These have worked reasonably well for me for years, though I did have a virtual machine struggle to do some builds when I ran too many make jobs in parallel and then a gargantuan compiler job came along and needed too much memory. However there was enough swap and eventually it thrashed its way through, and more importantly I was still able to run commands, albeit slowly, and my one large interactive process (emacs), sometimes took quite a while to wake up and respond. # N.B.: On a live system make sure to order changes to these values so that you # always lower any values from their default first, and then raise any that are # to be raised above their defaults. This way, the sum of the minimums will # stay within the 95% limit. # the minimum percentage of memory always (made) available for the # file data cache # # The default is 10, which is much too high, even for a large-memory # system... # vm.filemin=5 # the maximum percentage of memory that will be reclaimed from other uses for # file data cache # # The default is 50, which may be too high for small-memory systems but may be # about right for large-memory systems... # #vm.filemax=25 # the minimum percentage of memory always (made) available for anonymous pages # # The default is 10, which is way too low... # vm.anonmin=40 # the maximum percentage of memory that will be reclaimed from other uses for # anonymous pages # # The default is 80, which seems just about right, but then again it's unlikely # that the majority of inactive anonymous pages will ever be reactivated so # maybe this should be lowered? # #vm.anonmax=80 # the minimum percentage of memory always (made) available for text pages # # The default is 5, which may be far too low on small-RAM systems... # vm.execmin=20 # the maximum percentage of memory that will be reclaimed from other uses for # text pages # # The default is 30, which may be too low, esp. for big programs on small-memory # systems... # vm.execmax=40 # It may also be useful to set the bufmem high-water limit to a number which may # actually be less than 5% (vm.bufcache / options BUFCACHE) on large-memory # systems (as BUFCACHE cannot be set below 5%). # # note this value is given in bytes. # #vm.bufmem_hiwater= -- Greg A. Woods <gwoods%acm.org@localhost> Kelowna, BC +1 250 762-7675 RoboHack <woods%robohack.ca@localhost> Planix, Inc. <woods%planix.com@localhost> Avoncote Farms <woods%avoncote.ca@localhost>
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